For many years, the design of concrete structures imitated typical steel design of column, girder and beam. With technological advances in structural concrete, however, its own form began to evolve. Concrete has the advantages of lower cost than steel, of not requiring fireproofing, and of its plasticity, a quality that lends itself to free flowing or boldly massive architectural concepts. On the other hand, structural concrete, though quite capable of carrying almost any compressive (vertical) load, is extremely weak in carrying significant tensile loads. It becomes necessary, therefore, to add steel bars, called reinforcements, to concrete, thus allowing the concrete to carry the compressive forces and the steel to carry the tensile (horizontal) forces.
Structures of reinforced concrete may be constructed with load-bearing walls, but this method does not use the full potentialities of the concrete. The skeleton frame, in which the floors and roofs rest directly on exterior and interior reinforced-concrete columns, has proven to be most economic and popular. Reinforced-concrete framing is seemingly a quite simple form of construction. First, wood or steel forms are constructed in the sizes, positions, and shapes called for by engineering and design requirements. The steel reinforcing is then placed and held in position by wires at its intersections. Devices known as chairs and spacers are used to keep the reinforcing bars apart and raised off the form work. The size and number of the steel bars depends completely upon the imposed loads and the need to transfer these loads evenly throughout the building and down to the foundation. After the reinforcing is set in place, the concrete, a mixture of water, cement, sand, and stone or aggregate, of proportions calculated to produce the required strength, is placed, care being taken to prevent voids or honeycombs.
One of the simplest designs in concrete frames is the beam-and-slab. This system follows ordinary steel design that uses concrete beams that are cast integrally with the floor slabs. The beam-and-slab system is often used in apartment buildings and other structures where the beams are not visually objectionable and can be hidden. The reinforcement is simple and the forms for casting can be utilized over and over for the same shape. The system, therefore, produces an economically viable structure. With the development of flat-slab construction, exposed beams can be eliminated. In this system, reinforcing bars are projected at right angles and in two directions from every column supporting flat slabs spanning twelve or fifteen feet in both directions.
Reinforced concrete reaches its highest potentialities when it is used in pre-stressed or post-tensioned members. Spans as great as 100 feet can be attained in members as deep as three feet for roof loads. The basic principal is simple. In pre-stressing, reinforcing rods of high tensile strength wires are stretched to a certain determined limit and then high-strength concrete is placed around them. When the concrete has set, it holds the steel in a tight grip, preventing slippage or sagging. Post-tensioning follows the same principal, but the reinforcing is held loosely in place while the concrete is placed around it. The reinforcing is then stretched by hydraulic jacks and securely anchored into place. Prestressing is done with individual members in the shop and post-tensioning as part of the structure on the site.
In a typical tendon tensioning anchor assembly in such post-tensioning operations, there is provided a pair of anchors for anchoring the ends of the tendons suspended therebetween. In the course of installing the tendon tensioning anchor assembly in a concrete structure, a hydraulic jack or the like is releasably attached to one of the exposed ends of the tendon for applying a predetermined amount of tension to the tendon. When the desired amount of tension is applied to the tendon, wedges, threaded nuts, or the like, are used to capture the tendon and, as the jack is removed from the tendon, to prevent its relaxation and hold it in its stressed condition.
Metallic components within concrete structures may become exposed to many corrosive elements, such as de-icing chemicals, sea water, brackish water, or spray from these sources, as well as salt water. If this occurs, and the exposed portions of the anchor suffer corrosion, then the anchor may become weakened due to this corrosion. The deterioration of the anchor can cause the tendons to slip, thereby losing the compressive effects on the structure, or the anchor can fracture. In addition, the large volume of by-products from the corrosive reaction is often sufficient to fracture the surrounding structure. These elements and problems can be sufficient so as to cause a premature failure of the post-tensioning system and a deterioration of the structure.
Various attempts have been made in the prior art to reduce or eliminate the potential for corrosion within the wedge cavity of the anchor. For example, U.S. Pat. No. 5,024,032, entitled “Post-Tensioning Anchor” and issued to Rodriguez on Jun. 18, 1991, discloses a post-tension anchor and cap. The cap friction fits with the anchor in an effort to enclose the wedge cavity from external materials. The friction-fitting cap includes tabs or so-called “ears” around which securing filaments are tied. The securing filaments are purported to retain the cap within a press-fit engagement of the anchor, thereby precluding corrosives or contaminants from reaching the wedge cavity of the anchor.
U.S. Pat. No. 4,918,887, entitled “Protective Tendon Tensioning Anchor Assembly” and issued to Davis et al. on Apr. 24, 1990, discloses the combination of an anchor plate, a sealing cap and a resilient sealing ring. The combination is used in an effort to seal the wedge assembly of the anchor from the external environment. The combination represents a relatively complicated configuration for a sealing cap wherein various locking fingers and a specially shaped sealing ring are necessary in an effort to seal the wedge cavity of the anchor from external contaminants.
U.S. Pat. No. 4,773,198, entitled “Post-Tensioning Anchorages for Aggressive Environments”, and issued to Reinhardt on Sep. 27, 1988, discloses an alternative anchor and sealing cap assembly. The sealing cap is provided with threads for threading into a lip of the anchor plate for fluid sealing. Alternative seals such as “snap rings, bayonet fittings or other” fittings are also discussed.
U.S. Pat. No. 4,719,658, entitled “Hermetically Sealed Anchor Construction For Use In Post Tensioning Tendons”, and issued to Kriofske on Jan. 19, 1988, discloses an anchor and “plug” for fitting to the anchor. The plug includes a grease fitting through which grease may be injected, thereby forcing it into the cavities surrounding the anchor.
U.S. Pat. No. 5,440,842, issued on Aug. 15, 1995, to the present inventor, describes one technique for sealing and anchor. In this patent, a cap is provided with a O-ring seal disposed inwardly of a lip at the end of the cap. When the cap is pushed into the interior of the tubular section of the anchor, the elastomeric seal will engage the walls of the tubular section in a generally friction-fit relationship. As such, the cap will be retained properly in place. Unfortunately, this device could be easily dislodged or improperly placed. It is also possible that the cap could be improperly installed and this improper installation would not be noticeable upon inspection. As such, a need developed for a positive snap-fit connection between the cap and the anchor.
U.S. Pat. No. 6,023,894, issued on Feb. 15, 2000 to the present inventor also describes an improved cap connection for an anchor of a post-tension system. The improved cap has a flanged end adjacent to an open end of the tubular body of the cap. This flanged end has a circumferential surface. A locking member is formed on the circumferential surface for detachably engaging the protrusion such that the flanged end is fixedly received within the tubular section. A compressible seal is affixed within the polymeric encapsulation and extends around the end surface. The cap has an annular surface extending around the open end and in compressible contact with the compressible seal when the locking member engages the protrusion.
FIG. 1 is illustrative of a post-tension system of the prior art showing a typical cap connection. In particular, in FIG. 1, the post-tension system 10 includes a sealing cap 12 intended to be fitted in sealed relationship within the interior of the open end of the anchor 14. The anchor 14 supports the end 16 of a tendon. The tendon is locked in place with respect to the anchor 14 by wedges 18 and 20 disposed within a wedge cavity of the anchor 14. The anchor 14 includes an encapsulation 22 extending around a steel anchor body therein. The polymeric encapsulation 22 is encapsulated by injection molding the polymeric encapsulation 22 around the steel anchor body. A tubular section 24 is formed of the polymeric encapsulation 22 and extends outwardly of the anchor body. A rigid ring 26 is secured by injection molding the polymeric encapsulation 22 over the rigid ring 26. The rigid ring 26 is illustrated at having a smooth inner surface facing the tendon 16.
In FIG. 1, it can be seen that the anchor 14 includes a rear tubular member 28 which communicates with the tubular section 24. An extension tube 30 will fit in snap-fit connection or in friction-fit relationship over the rear tubular member 28. The extension tube 30 overlies a sheath 32 which encases the tendon 16 (the end 16 of which is shown protruding outwardly from the wedge cavity of the anchor 14). Although not shown, the end of the extension tube 30 overlying sheath 32 is sealed, by the use of tape or other means.
The sealing cap 12 is constructed of a high-density polyethylene or polypropylene material. The sealing cap 12 includes a tubular body 34 for covering the exposed end of the tendon 16 and, if required, for retaining a rust inhibitor chemical. The sealing cap 12 includes an outer lip 36 which will be ins surface-to-surface sealing friction-fit contact with the interior surface of the rigid ring 26 once the sealing cap 12 is connected to the anchor 14. The sealing cap 12 also includes an outer ridge 38 and an O-ring seal 40.
Unfortunately, with this prior art, the cap 12 is not “positively” attached within the tubular section 24 of the polymeric encapsulation 22 of anchor 14. Although this system has proven effective in preventing liquid intrusion into the interior of the anchor 14, construction engineers have required more positive connection between the sealing cap 12 and the anchor 14. By virtue of the friction-fit relationship between the sealing cap 12 and the anchor 14, it is possible for the sealing cap 12 to become dislodged by forces applied to the tubular body 34 of the sealing cap 12. In other circumstances, the O-ring seal 40 will not be positively engaged against the inner surface of the rigid ring 26. As such, a need developed so as to establish a more secure and positive relationship between the cap and the tubular section 24 of the anchor 14.
It is an object of the present invention to provide an improved cap and anchor which assures a positive connection between the cap and the anchor.
It is another object of the present invention to provide an improved cap and anchor that assures the liquid-tight engagement of the cap with the anchor.
It is a further object of the present invention to provide an improved cap which cannot be easily removed without a positive intended action for removal from the anchor.
It is still another object of the present invention to provide an improved cap which is easy to install into the anchor.
It is still a further object of the present invention to provide an improved cap and anchor which is easy to manufacture, easy to use, and relatively inexpensive.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.